The present invention relates to the method for forming an interconnection in a semiconductor element.
Increasing attention is paid to Cu which is regarded as the next generation interconnection material in the place of the A1 interconnection. The reason for this is that Cu has an excellent electromigration (EM) tolerance as well as small resistance of 1.69 micro ohm cm. However, increase in the current density with downsizing interconnections to microstructure requires the reinforcement of Cu to secure high reliability. One way to make the Cu film highly immune to electromigration is to improve crystalline properties of the Cu film. Therefore, the use of the underlayer texture of TiN film with strong TiN (111) orientation is effective. This is because Cu (111) crystallographic orientation is enhanced on TiN film having strong TiN (111) orientation. (reference document: Extended Abstracts of the 1997 International Conference On Solid State Devices and Materials 1997 pp 298-299)
Of late years, the chemical mechanical polishing (CMP) technology introduced for flattening the insulator film begins to be used for forming the Cu interconnections by the Damascene method. Forming an interconnection by the damascene method solves the problem that minute forming of an interconnection by reactive ion etching (RIE) is difficult in case of Cu. In addition, it is advantageous in that the strong coatability of an interlayer film to the step construction is not necessarily indispensable.
However, unlike the formation of an interconnection by the conventional reactive ion etching processing, it is considered that an interconnection formed by the damascene method is influenced by the crystal of the underlying film at the sidewall of the Cu interconnection as well as at the bottom surface thereof. For example, the Cu grain was classified into two. One which faces the sidewalls is classified as the edge region, whereas the other part is classified as the central region. Then, the Cu grain orientation of each region is analyzed. The width of the interconnection of the analytical object is 5 micrometers, and the average grain size of Cu is 0.9 micrometers.
The result of the analysis shows that Cu grains of Cu (111) orientation are decreased in the edge region compared with the central region. This supports the above-mentioned remark. Moreover, it is also well known that narrower width of the interconnection reduces a effect of improvement of a crystalline of the Cu film obtained by using said underlying film.